Spaghetti Nebula (Sh2-240)

Sh2-240: The Ghostly Web of an Exploded Star

Located on the border between the constellations Taurus and Auriga, Sh2-240, also known as Simeis 147, is a vast and complex supernova remnant. Despite its immense angular size—nearly three degrees across, or about six times the apparent size of the full Moon—this structure is barely visible in optical light, requiring advanced imaging techniques to reveal its faint filaments of ionized gas.

Discovery and Classification

Simeis 147 was first identified in 1952 by Soviet astronomers Grigory Shajn and Vera Gaze at the Simeis Observatory. Using a Schmidt telescope equipped with narrowband filters, they recorded deep photographic plates that revealed a large, faint nebulous structure. It was subsequently included in the Sharpless Catalogue of H II regions as Sh2-240. Later spectroscopic studies and radio observations revealed that the object is not an ionized hydrogen region but a supernova remnant.

According to Deep Sky Corner, “Simeis 147 (SNR G180.0–01.7) is an optically faint shell-type supernova remnant... Its age is estimated to ~40,000 years and one of the oldest SNRs with well-defined shell structure.”

Main Characteristics

Sh2-240 is situated at an estimated distance of approximately 1,470 parsecs, or about 4,800 light-years from Earth. It spans a physical diameter of around 150 light-years, making it one of the larger known supernova remnants in the Milky Way. The remnant is nearly spherical in geometry but is highly fragmented. Its apparent faintness and large angular size make it a challenging object for observation, requiring sensitive imaging and long exposures.

The remnant is expanding at an average velocity of around 80–120 km/s. Based on optical and radio data, the estimated kinetic energy from the original explosion lies near 10⁵¹ ergs, consistent with a typical core-collapse supernova (Sofue et al. 1980, Publications of the Astronomical Society of Japan).

Structure and Composition

The structure of Sh2-240 is predominantly filamentary, consisting of long, narrow strands of ionized gas shaped by the interaction of shock waves with the surrounding interstellar medium. These filaments are composed of hydrogen-alpha (Hα), doubly ionized oxygen (OIII), and singly ionized sulfur (SII). Optical and narrowband imaging highlight these components clearly, especially Hα emission, which traces the high-energy front of the expanding shell.

Radio observations reveal a diffuse, non-thermal continuum structure confirming the presence of synchrotron radiation—charged particles spiralling along magnetic fields—typical of mature supernova remnants. The radio morphology closely follows the optical filamentary shell, indicating strong magnetic field alignment. Additionally, studies using ROSAT and confirmed by data from XMM-Newton, have detected soft X-ray emission associated with hot, shocked plasma in the remnant’s interior (Leahy & Tian 2007, Astronomy & Astrophysics).

Stellar Population

At the core of the remnant lies a compact object: PSR J0538+2817, a young, rotation-powered pulsar identified in the early 1990s and confirmed in 1994 through Arecibo observations. It has a spin period of 143 milliseconds and a transverse velocity of nearly 400 km/s.

The alignment of its proper motion with the centre of the SNR, as well as the close match in age and distance, strongly support a common origin. The supernova left behind this runaway neutron star, offering a clear and direct connection between core-collapse supernovae and pulsar formation.

The star that exploded to form Sh2-240 was likely a high-mass progenitor (≥ 8 solar masses), though the exact spectral type remains unknown due to the lack of associated stellar clusters or pre-supernova imaging. 

Scientific Relevance

Sh2-240 continues to be studied for insights into the long-term evolution of supernova remnants. Its filamentary morphology, advanced age, and low surface brightness make it a benchmark for investigating late-phase SNR dynamics, radiative shock cooling, and the role of remnants in interstellar medium enrichment. The presence of a known pulsar adds a rare opportunity to model the spatial and temporal relationship between neutron stars and their parent supernovae.

Moreover, in a 2001 study by Kramer et al. (Astrophysical Journal), detailed timing observations of PSR J0538+2817 helped constrain neutron star birth velocities and cooling mechanisms, both of which are critical for understanding stellar evolution in post-supernova environments.

Future Evolution

Over the coming tens of thousands of years, Sh2-240 will continue to expand and gradually dissipate. The filaments will lose coherence, and the shocked gas will cool and mix with the ambient interstellar medium. The remnant’s energy will fade into the galactic background, leaving only PSR J0538+2817 as a long-lived relic of the original explosion. The material ejected by the supernova will contribute to the cycle of matter in the galaxy, potentially seeding future star formation.

The Remote AstroPals Project

The Spaghetti Nebula was selected as the subject of the first imaging project by Remote AstroPals, a brand-new initiative created together with my friends Massimo and Aygen. Our aim is to connect amateur astronomers from around the world through shared imaging campaigns and scientific collaboration. One of our core motivations is to break geographical barriers in astrophotography and foster a sense of global community around a shared passion.

Data for this inaugural project was acquired remotely via Telescope Live, using a Takahashi FSQ-106EDX4 telescope equipped with Astrodon LRGB + narrowband (Hα, OIII) filters. Although the data presented several challenges—such as strong gradients and less-than-ideal calibration—we successfully processed the dataset and revealed the intricate filamentary structure of this expansive supernova remnant. Post-processing was carried out individually using PixInsight before the single images were stacked together for this incredible final image.

Despite the suboptimal conditions, the project delivered meaningful results, laying the foundation for future work. We are now working on our second project and actively welcoming new members who share our passion for collaborative astrophotography, open science, and global outreach.

Observing Sh2-240

Sh2-240 lies close to the star Elnath (Beta Tauri), a bright marker shared by the constellations Taurus and Auriga. The remnant covers a wide area near this region and is best observed from November through February in the Northern Hemisphere. Visual observation is not feasible due to its extremely low brightness, but astrophotographers equipped with narrowband filters (particularly Hα, SII, and OIII), fast wide-field telescopes, and long total exposure times can successfully capture its structure from their backyards.

Reference List

1. Deep Sky Corner. Simeis 147 – Supernova Remnant in Taurus
2. Constellation Guide. The Spaghetti Nebula (Simeis 147)
3. Leahy, D.A. & Tian, W.W. (2007). “A Study of the Supernova Remnant S147 (G180.0–1.7) and Its Pulsar.” Astronomy & Astrophysics, 461:1013–1019
4. Anderson, S.B. et al. (1996). Discovery of the Pulsar J0538+2817 in the Supernova Remnant S147
5. Sofue, Y., et al. (1980). “Radio Observations of S147.” Publications of the Astronomical Society of Japan
6. Kramer, M. et al. (2001). The Proper Motion, Age, and Initial Spin of PSR J0538+2817
7. ATNF Pulsar Catalogue. PSR J0538+2817
8. NASA/IPAC Extragalactic Database (NED). Simeis 147
9. ESA/Hubble. Images of Simeis 147  
10. Watch This Spaceman. Supernova Sensation: Imaging Simeis 147